1. Field of the Invention
The present invention relates to a process for making polyalkyldiallylamine-epihalohydrin resins, the resultant resins, and their uses as wet strength additives for papermaking.
2. Description of Background and Other Information
Polyamidoamine-epichlorohydrin resins (PAE resins), polyalkylenepolyamine-epichlorohydrin resins (PAPAE resins), amine polymer-epichlorohydrin resins, polyurylene-epichlorohydrin resins, polyamide-polyurylene-epichlorohydrin resins, and combinations of these resins with anionic polymers such as carboxymethyl cellulose (CMC), have been widely used in the manufacture of paper having high levels of wet strength.
Polyamine-epihalohydrin resins are cationic thermosetting materials widely used to increase the wet strength of papers, however these materials often contain large quantities of epihalohydrin hydrolysis products. For example, commercial polyaminopolyamide-epichlorohydrin resins typically contain 1-10wt % (dry basis) of the epichlorohydrin (epi) by-products, 1,3-dichloropropanol (1,3-DCP), 2,3-dichloropropanol (2,3-DCP) and 3-chloropropanediol (CPD). There has been a movement within the industry to produce wet-strength resins having lower levels of adsorbable organic halogen (AOX) species, including, epichlorohydrin and epichlorohydrin by-products such as 1,3-dichloropropanol, 2,3-dichloropropanol and 3-chloropropanediol as well as an organic halogen bound to the polymer backbone. When residual alkyldiallylamine monomers are present during the reaction of an ADAA polymer with epichlorohydrin, the reaction product of epichlorohydrin with ADAA monomer produces an organohalogen compound that will be an AOX contributor. Thus, even when using the hydrohalide salt of a polyalkyldiallylamine (pADAA) to prepare pADAA-epichlorohydrin resins, there is still a need in the industry to reduce the residual epihalohydrin hydrolysis products to the lowest attainable level.
Among the epihalohydrin-containing resins, the tertiary amine-based epoxide resins provide the highest resin efficiency (which generally refers to the amount of wet strength developed per unit mass added to the paper or that overall higher levels of wet strength result regardless of how much resin is added) as well as the highest off-machine wet strength (the ability to provide wet strength to a sheet of paper without aging). This is in contrast to most other wet strength resins which show an improvement in wet strength after aging for several days. The tertiary amine-based epoxide resins give high levels of wet strength as made, which doesn't change much with time. Of the various types of tertiary amine-based epoxide resins that have been described, the polymethyldiallylamine-epichlorohydrin resins are the most effective wet strength additives known for paper on a weight basis. A number of these resins have been previously described, as set forth below. Although these resins are quite effective in imparting wet strength to paper, there is still a need for additives that (1) provide a high level of wet strength in paper, (2) have low levels of residual epichlorohydrin hydrolysis products in the resin and in paper products made using these resins and (3) are resins having lower levels of adsorbable organic halogens (AOX).
Polyalkyldiallylamine-epichlorohydrin resins and variants thereof have been disclosed in a number of U.S. patents, for example, U.S. Pat. No. 3,686,151 (Keim); U.S. Pat. No. 3,700,623 (Keim); U.S. Pat. No. 3,772,076 (Keim); U.S. Pat. No. 3,833,531, (Keim); U.S. Pat. No. 4,222,921 (Van Eenam); U.S. Pat. No. 4,233,417 (Van Eenam); U.S. Pat. No. 4,298,639 (Van Eenam); U.S. Pat. No. 4,340,692 (Van Eenam); U.S. Pat. No. 6,111,032 (Bower); and U.S. Pat. No. 6,268,452 (Kato et al.).
In addition, the use of polyamidoamine-epihalohydrin resins and other types of polyamine-epihalohydrin resins as wet strength agents is well known, wherein much of the discussion centers around reducing the levels of epihalohydrin hydrolysis products in these resins, for example, as described in U.S. Pat. No. 5,171,795 (Miller et al.) and U.S. Pat. No. 5,017,642 (Hasegawa et al.).
Post-synthesis treatments of resins to reduce the levels of hydrolysis products or halogenated by-products has also been described, for example as set forth in U.S. Pat. No. 5,256,727 (Dulaney et al.), U.S. Pat. No. 5,516,885 (Gorzynski et al.) and WO 92/22601.
The present invention provides for the preparation of polyalkyldiallylamine-epihalohydrin resins from the hydrohalide salt form of the alkyldiallylamine polymer. These hydrohalide salt-based resins are advantageous because such resins show superior performance as wet strength additives in paper when compared to the performance of resins prepared using other acid salts of the alkyldiallylamine polymer.
Another advantage in using the hydrohalide salt of the alkyldiallylamine polymer, specifically, the hydrochloride salt of polymethyldiallylamine, is that such resins are approved by the Food and Drug Administration (FDA) in the United States as a paper additive suitable for use in food contact applications (21 CFR Ch. I; 176.170).
In addition, the papermaking process releases epihalohydrin hydrolysis products into the environment, wherein the hydrolysis products can be found in the water that was used to make the paper, and/or in the air due to evaporation that occurs when the paper is dried. The hydrolysis products can also be found in the paper itself. Thus, the present invention addresses a need in the industry to reduce the levels of hydrolysis products found in paper, thereby helping to reduce and control these emissions in the environment to as low a level as possible.